This invention relates in general to printing and more particularly to a machine for applying coatings to printed webs in a printing press.
The cover and pages of a typical high quality magazine are usually printed on a four color offset printing press in which the four colors are applied successively to webs of paper that are run through the press at high speed. After emerging from the press, each web is severed and folded to form individual signatures, and these signatures are then loaded into a binding machine where they are with other signatures combined into the individual copies of the magazine. The typical four color printing press has a separate print stand for each color, and these stands are aligned and synchronized with each other such that a single web passing through them acquires a succession of impressions which combine to produce a four color print. In addition to the printing stands, the typical printing press has a dryer into which the web passes upon emerging from the last printing stand, and within this dryer the web is heated to volitilze the solvents within the ink. Even so, the printed impression will smear while the web remains hot, so many presses have chill roll stands beyond their dryers to cool the web and thereby render the full color printed impressions fast. Some sort of slitting and stacking machine is usually located beyond the chill roll stand to sever the webs and fold the severed segments in order to produce individual signatures which are thereafter stacked.
Certain portions of a magazine encounter more abuse than others, and perhaps no portion encounters more than the cover. For example, magazines are often arranged in bundles with one magazine stacked on top of another. During shipment the covers of these magazines shift or slide relative to each other, and this movement may partially obliterate the printed impression. Yet the cover is the portion of the magazine which the reader or potential purchaser first observes, and for this reason publishers put a great deal of thought and effort into preparing covers. Obviously, they want the covers of their publications to be attractive. To this end, printers on occasion apply a varnish or some other coating to the covers of the magazines that they print. This varnish, being considerably harder than the paper over which it extends, protects the printed impression, and further imparts a glossing texture to the cover so as to enhance its appearance.
Some printers engage outside contractors to apply the varnish, but this presents still another step in an already complex procedure and as such delays the production and significantly increases the cost. Others apply the varnish at the printing presses, but heretofore no truly satisfactory machines have been available for this procedure. Some coating machines of current construction employ the gravuer principle in that the coating is transferred directly from a plate cylinder to the web. Often the coating is not uniform and somewhat blemished. Moreover, this type of transfer does not lend itself to spot coating, that is leaving some areas of the cover free of the coating so that additional material, such as a subscribers' name and address or perhaps the price, may be subsequently printed on the publication. Moreover conventional coating machines occupy considerable space, usually at the end of a press beyond the chill roll stand, but space is usually at a premium in printing plants. Some coating machines of current construction fit on the actual press, but these machines apply the coating directly over the wet ink. This detracts from the quality of the printed impression, and to a measure counteracts the effects of the glossy texture. Others, are mounted beyond the press where they occupy considerable floor space that could be put to other uses. These machines rely on ultraviolet light from an ultraviolet source that is within the machine itself to dry the coating.